Phase contrast imaging using X-rays is based on a grating-based interferometer that uses the Talbot effect for imaging. For this purpose, two gratings are positioned parallel to one another perpendicularly to the X-ray beam. The phase grating g1 consists of lines that cause a phase shift of Pi (or Pi/2) and negligible X-ray absorption. The diffracted rays interfere in accordance with the fractional Talbot effect and an interference pattern arises which is periodic in the directions perpendicular to the grating lines. The second grating serves for analyzing the interference image and is intended to absorb the X-ray radiation as well as possible [absorption grating] (absorption greater than 50% is at least necessary for image evaluation).
The publications by Franz Pfeiffer et al., “Phase retrieval and differential phase-contrast imaging with low-brilliance X-ray sources”, Nature Physics, Vol. 2, April 2006, pages 258-261 and “Hard X-ray dark-field imaging using a grating interferometer”, Nature Materials, Vol. 7, February 2008, pages 134-137 describe the possibilities of phase contrast X-ray imaging and dark-field imaging using non-coherent X-ray sources. In order to realize these imaging systems, it is necessary to realize grating structures with periods in the range of a few micrometers, the transmission of which over the relevant energy range is less than 50%. The relevant energies are defined by the respective application. Human-medical X-ray examinations of the whole body are usually carried out at working energies of between 50 and 90 keV. In the case of a smaller thickness of the objects to be penetrated, e.g. CTs on children, energies of less than 50 to 70 keV are often also of interest. Thus, lower energies can be used in mammography, for example. The energy is lower in small-animal tests, too. Furthermore, it should be taken into consideration that owing to the radiation emitted by an X-ray tube, even at a high “working energy”, radiation below the working energy cannot be avoided.
Gratings used nowadays use gold as material that greatly absorbs the X-rays. Owing to the atomic structure, the absorption of gold decreases by a factor of 4 below an X-ray energy of 80.7 keV. Accordingly, in particular wide-band exposures with X-ray light in a range above and below an X-ray energy of 80 keV do not lead to satisfactory results.
The production of gratings has hitherto been published using gold by means of the LIGA method (Reznikova, E.; Mohr, J.; Boerner, M.; Nazmov, V.; Jakobs, P. J., Soft X-ray lithography of high aspect ratio SU8 submicron structures, Microsystem Technologies, 14 (2008), pages 1683-88 and conformal coating of Si structures with gold in an electrochemical gold bath (C. David, J. Bruder, T. Rohbeck, C. Grünzweig, C. Kottler, A. Diaz, O. Bunk, F. Pfeiffer, Fabrication of diffraction gratings for hard X-ray phase contrast imaging. Microelectric Engineering 84 (2007) 1172-1177), wherein the Si structures are produced by means of a DRIE process.
P. Ramm, M. J. Wolf, A. Klumpp, R. Wieland, B. Wunderle, B. Michel, Through Silicon Via Technology—Processes and Reliability for Wafer-Level 3D System Integration, Proc. 2008 Electronic Components and Technology Conference, pp. 841 discloses technical processes appertaining to silicon technology for producing structures with tungsten.
The production of comparable structures from lead is likewise known (V. Lehmann, S. Rönnebeck, MEMS techniques applied to the fabrication of anti-scatter grids for X-ray imaging, Sensors and Actuators, A95 (2002), 202-207).
The problem of very low absorption of gold below the 80.7 keV edge has not been addressed hitherto.